Cellulose ester solutions



Unite poration of Delaware N Drawing. Filed June 9, 1959, Ser. No.819,006 16 Claims. (Cl. 106-178) This invention relates to improvedcellulose ester solutions.

Fibers and films of a cellulose ester are conventionally formed from asolution of the cellulose ester in an appropriate solvent. Varioussolvents are used for this purpose depending on the chemical nature ofthe cellulose ester. For example, there are two main types of celluloseacetate in commercial production, the secondary acetate which has anacetyl value below about 55% by weight as acetic acid, and the primaryacetate or so-called triacetate which has an acetyl value above about59%. In forming fibers and films, the secondary acetate is commonlydissolved in acetone and the triacetate in a mixture of methylenechloride and an alcohol such as methanol. While solutions prepared withthese solvents are satisfactory in most respects, it maybe preferred insome instances to obtain solutions of cellulose acetate or othercellulose esters in solvents having somewhat different properties. Morespecifically, if it is desired to build a plant without extensiveventilating equipment, a solvent having reduced volatility andinllamrnability would be beneficial. In the case of cellulosetriacetate, it may be desired to avoid the equipment necessary for therecovery of two separate solvent components. Furthermore, if wetspinning is employed, it may be advantageous to employ a solvent suchthat the extruded solution does not coagulate too rapidly thus allowingample time for the filaments to be stretched and oriented. Finally it isoften desired to form fibres and films from mixtures of cellulose estersand high polymeric materials of substantially different chemicalstructure, so that there is considerable need for solvents which arecapable of dissolving both types of material.

It is an object of this invention to provide solutions of celluloseesters in relatively non-volatile solvents having reducedinflammability. It is a further object to provide solutions of celluloseesters in solvents which may be more easily recovered. It is a stillfurther object to provide solutions of cellulose esters which coagulateless readily when wet spun so that the resulting filaments may be moreeasily stretched and oriented. It is a still further object of thisinvention to provide solutions of cellulose esters and other highpolymeric materials which may be extruded into fibers and films. Furtherobjects will become apparent from the following description of theinvention.

In accordance with one aspect of the invention, the cellulose ester isdissolved in a solvent comprising a straight chain, aliphatic carboxylicacid'or an ester of such an acid, said acid or ester containing atleast'one halide, sulfide or ethylenically unsaturated radical, or ahalogensubstituted straight chain, aliphatic carboxylic acid nitrile.

- It has been found that these solvents are" capable of forming clear,gel-free solutions of desirable concentration and viscosity which arecapable of being formed into useful One group of contemplated solventsare the halogensubstituted straight chain, aliphatic carboxylic acid,e.g.

halogen-substituted fatty acids such as dichloroacetic acid,trifiuoroacteic acid, and beta-chloropropionic acid (as a saturatedsolution in water.) The acid preferably has up to four carbon atoms.Also contemplated are alkyl esters of these acids, e.g. methylchloroacetate, ethyl chlo- 3,038,8l4 Patented June 12, 1962 roacetate,methyl beta-chloropropionate and methyl alpha-chloropropionate.

Another group of compounds useful as solvents for cellulose esters arethe halo-lower alkyl esters of straight chain, aliphatic carboxylicacids, e.g. of fatty acids, such as 2-chloroethyl acetate, chlorornethylacetate, fluoromethyl acetate and 2-fluoroethyl acetate.

A further group of contemplated solvents are halogensubstituted straightchain, aliphatic carboxylic acid nitriles, e.g. nitriles ofhalogen-substituted fatty acids such a beta-chloropropionitrile andchloroacetonitrile.

A still further group of compounds suitable as solvents for celluloseesters are straight chain, aliphatic carboxylic acids containing asulfide radical, e.g. mercapto-substituted fatty acids such asthioglycolic acid.

Also contemplated as solvents are ethylenically unsaturated, straightchain, aliphatic carboxylic acids. A preferred group of compounds aremonoethylenically unsaturated acids, e.g. alkenyl carboxylic acids suchas acrylic acid, and alpha-crotonic acid (in water solution). Theunsaturated acid preferably has up to four carbon atoms.

The compounds useful as solvents are preferably liquid at roomtemperature, e.g. 22 (3., especially when used as the sole solvent.While solutions of cellulose acetate, especially the triacetate, areparticularly suitable, other cellulose esters may also be dissolved inthe solvents of this invention, e.g. cellulose carboxylic acid esterssuch as cellulose acetate, cellulose propionate, cellulose butyrate andmixed esters such as cellulose acetate-propionate and celluloseacetate-butyrate.

The cellulose ester may be dissolved in some of the solvents, e.g.halogen-substituted fatty acids, with another high polymeric material,e.g. high molecular weight linear polyesters of polycarboxylic acids andpolyhydric alcohols such as polyethylene terephthalate, and highmolecular weight linear polycarbonamides such as polyhexarnethyleneadipamide, to form solutions which may be used to form fibers and filmsof the mixed polymeric material. If a polymeric component other than acellulose ester is used it may be present in an amount, for example, of1 to 80 percent by weight of the total polymeric material, depending onthe specific nature of the other polymeric material.

Solutions of a cellulose ester and if desired another polymericcomponent may be formed having a wide range of concentration andviscosity, e.g. 1 to percent by weight of total polymeric material basedon the Weight of the composition and a Brookfield viscosity at 22 C. of300 to 7000 poises. If desired, the solvent of this invention may bemixed with other compounds to form a solvent mixture, the nature of thecompounds depending on which solvent under the invention is being used.For example, beta-chloropropionic acid may be used as an aqueoussolution.

The solution is formed into shaped articles such as fibers and films bysubjecting it in a form having a crosssection with at least one thindimension to a medium whereby the polymeric material is separated frommost of the solvent and thus coagulated or precipitated. This may bedone by contacting the solution with an atmosphere whereby the solventis evaporated, e.g. as in casting or dry spinning, or by extruding thesolution, as in wet spinning, into a liquid medium which is annonsolvent for the polymeric material i.e. a coagulant or precipitant,such as liquids having a large proportion of water or methanol.

The invention is further illustrated by the following examples:

Example I Cellulose triacetate having an acetyl value of 61.5%

by weight and an intrinsic viscosity of 2.0 was dissolved at roomtemperature by stirring in dichloroacetic acid to yield a solution of10% by weight of cellulose triacetate. The solution was clear,transparent, gel-free and had a Brookfield viscosity at 22 C. of 1040poises. Satisfactory films could be cast from this solution.

Example 11 The same cellulose triacetate as in Example I was dissolvedin methyl chloroacetate at room temperature to yield solutions of 13%,15% and 20% by weight of cellulose triacetate. The Brookfieldviscosities of the solutions at 22 C. were 1200 poises for the 13%solution, 3050 poises for the 15% solution, and 7000 poises for the 20%solution. The solutions were gel-free and transparent and could be castinto films which were also perfectly transparent and flexible and showedconsiderable toughness and resistance to bending. In addition,monofilaments could be extruded from a 0.1 mm. hole spinnerette intowater which coagulated slowly even at 90 C.

Example III The cellulose triacetate of Example I was dissolved at roomtemperature in ethyl chloroacetate to yield a solution of 10% by weightof triacetate. Its Brookfield viscosity at 22 C. was 480 poises and itcould be cast into satisfactory films.

Example IV The cellulose triacetate of Example I was dissolved at roomtemperature in 2-chl0roethyl acetate to yield a solution having 10% byweight of triacetate. Its Brookfield viscosity at 22 C. was 480 poisesand it could be cast into satisfactory films.

Example V The cellulose triacetate of Example I was dissolved at roomtemperature in beta-chloropropionitrile to yield a solution of 10% byweight of triacetate. Its Brookfield viscosity at 22 C. was 300 poisesand it could be cast into satisfactory film.

Example VI The cellulose triacetate of Example I was dissolved at roomtemperature in thioglycolic acid to yield a solution of 10% by weight oftriacetate. Its Brookfield viscosity at 22 C. was 1080 poises and itcould be cast into satisfactory film.

Example VII The cellulose triacetate of Example I was dissolved intrifluoroacetic acid at room temperature to yield a solution of 10% byweight of triacetate, having a Brookfield viscosity to 22 C. of 700poises. The solution was clear and gel-free and could be cast intosatisfactory film.

Example VIII The cellulose triacetate of Example I was dissolved at roomtemperature in acrylic acid to yield a solution of 10% by weight oftriacetate having a Brookfield viscosity at 22 C. of 1000 poises. Thesolution was clear and could be cast into satisfactory films.

Example IX A mixture of 50% by weight of the cellulose triacetate ofExample I and 50% by weight of polyethylene terephthalate was dissolvedin dichloroacetic acid at room temperature to yield a solution of 10% byweight of total polymeric material having a Brookfield viscosity at 22C. of 1700 poises. Film obtained by the coagulation of the dope in hotwater dried with no shrinkage and was flexible.

Example X A mixture of 0% by weight of the cellulose triacetate ofExample I and 50% by Weight of polyhexamethylene adipamide was dissolvedin dichloroacetic acid to give a 4 solution of 10% by weight of totalpolymeric material having a Brookfield viscosity at 22 C. of 1700poises. Satisfactory films of the mixed polymeric material could beobtained by coagulating the dope in hot water.

It is to be understood that the foregoing detailed description is givenmerely by way of illustration and that many variations may be madetherein without departing from the spirit of my invention.

Having described my invention what I desire to secure by Letters Patentis:

l. A solution of a cellulose carboxylic acid ester in a solventconsisting essentially of a compound selected from the group consistingof straight chain, lower aliphatic carboxylic acids and esters of saidacids, said acids and esters containing at least one member of the groupconsisting of halide, sulfide, and ethylenically unsaturated radicals,and halogen-substituted lower carboxylic acid nitriles.

2. A solution of a cellulose acetate in a solvent consisting essentiallyof a compound selected from the group consisting of straight chain,lower aliphatic carboxylic acids and esters of said acids, said acidsand esters containing at least one member of the group consisting ofhalide, sulfide, and ethylenically unsaturated radicals, andhalogen-substituted lower carboxylic acid nitriles.

3. A solution of a cellulose acetate in a solvent consisting essentiallyof a halogen-substituted, straight chain, lower fatty acid.

4. A solution of a cellulose acetate in a solvent consisting essentiallyof an alkyl ester of halogen-substituted, straight chain, lower fattyacid.

5. A solution of a cellulose acetate in a solvent consisting essentiallyof a haloalkyl ester of a straight chain, lower fatty acid.

6. A solution of a cellulose acetate in a solvent consisting essentiallyof a halogen-substituted, straight chain, lower fatty acid nitrile.

7. A solution of a cellulose acetate in a solvent consisting essentiallyof a mercapto-substituted, straight chain, lower fatty acid.

8. A solution of a cellulose acetate in a solvent consisting essentiallyof a straight chain, aliphatic alkenyl carboxylic acid containing up tofour carbon atoms.

9. A solution of cellulose acetate according to claim 3 containing ahigh molecular weight linear polyester of a polyhydric alcohol and apolycarboxylie acid, said polyester being present in an amount of 1 topercent by weight of the weight of the total polymeric material.

10. A solution of cellulose acetate according to claim 3 containing ahigh molecular weight linear polycarbonamide present in an amount of 1to 80 percent by weight of the weight of the total polymeric material.

11. A method of forming fibers and films of a cellulose acetate whichcomprises dissolving said cellulose acetate in a solvent consistingessentially of a compound from the group consisting of a straight chain,lower aliphatic carboxylic acids and esters of said acids, said acidsand esters containing at least one member of the group consisting ofhalide, sulfide and ethylenically unsaturated radicals, andhalogen-substituted lower carboxylic acid nitriles, and separating mostof said solvent from said solution in a form having a cross-section withat least one thin dimension.

12. A method according to claim 11 wherein the solvent consistsessentially of a halogen-substituted, straight chain, lower fatty acid,and the solution further contains a high molecular weight linearpolyester of a polyhydric alcohol and a polycarboxylic acid.

13. A method according to claim 11 wherein the solvent consistsessentially of a halogen-substituted, straight chain, lower fatty acid,and the solution further contains a high molecular weight linearpolycarbonamide.

14. A method of forming fibers of a cellulose acetate which comprisesdissolving said cellulose acetate in a solvent consisting essentially ofa compound from the group consisting of a straight chain, loweraliphatic carboxylic acids and esters of said acids, said acids andesters containing at least one member of the group consisting of halide,sulfide and ethylenically unsaturated radicals, and halogen-substituted,lower carboxylic acid nitriles, and extruding the resulting solution inthe shape of filaments into a liquid medium which is a non-solvent forsaid cellulose acetate.

15. A solution of cellulose triacetate having an acetyl value above 59%by weight calculated as combined acetic acid in a solvent consistingessentially of a compound selected from the group consisting of straightchain, lower aliphatic carboxylic acids and esters of said acids, saidacids and esters containing at least one member of the group consistingof halide, sulfide, and ethylenically unsaturated radicals, andhalogen-substituted, [lower carboxylic acid nitriles.

16. A solution according to claim 3 wherein said acid isbeta-chloropropionic acid and said acid is mixed with water.

References Cited in the file of this patent UNITED STATES PATENTS2,336,310 Spence et a1. Dec. 7, 1943 2,346,350 Berl et a1. Apr. 11, 19442,350,300 Bogin May 30, 1944 2,362,182 Baker Nov. 7, 1944 2,542,402Easton Feb. 20, 1951 2,607,703 Resch et a1. Aug. 19, 1952 2,812,267Garner et a1. Nov. 5, 1957 2,902,383 Beste Sept. 1, 1959 OTHERREFERENCES Ott et a1.: High Polymers, vol. V, part II (1954), pages 794and 795.

Ott et al.: High Polymers, Vol V, part III (1955), pages 1454-1456.

Brice et al.: Chem. and Eng. News, vol. 3 (1953), pages 20 510-513 (TP 1I 418).

1. A SOLUTION OF A CELLULOSE CARBOXYLIC ACID ESTER IN A SOLVENTCONSISTING ESSENTIALLY OF A COMPOUNF SELECTED FROM THE GROUP CONSISTINGOF STRAIGHT CHAIN, LOWER ALIPHATIC CARBOXYLIC ACIDS AND ESTERS OF SAIDACID, SAID ACIDS AND ESTERS CONTAINING AT LEAST ONE MEMBER OF THE GROUPCONSISTING OF HALIDE, SULFIDE, AND ETHYLENICALLY UNSATURATED RADICALS,AND HALOGEN-SUBSTITUTED LOWER CARBOXYLIC ACID NITRILES.